If you use the [[EclipseLink/UserGuide/JPA/Basic JPA Development/Mapping/Entity/GeneratedValue|<tt>@GeneratedValue</tt> annotation]] to specify a primary key generator of type <tt>TABLE</tt>, then you can use the <tt>@TableGenerator</tt> annotation to fine-tune this primary key generator to do the following:

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If you use the [[EclipseLink/UserGuide/JPA/Basic JPA Development/Entities/Ids/GeneratedValue|<tt>@GeneratedValue</tt>]] annotation to specify a primary key generator of type <tt>TABLE</tt>, then you can use the <tt>@TableGenerator</tt> annotation to fine-tune this primary key generator to do the following:

* change the name of the primary key generator's table, because the name is awkward, a reserved word, incompatible with a preexisting data model, or invalid as a table name in your database;

* change the name of the primary key generator's table, because the name is awkward, a reserved word, incompatible with a preexisting data model, or invalid as a table name in your database;

<td>By default, EclipseLink persistence provider assumes that none of the columns in the primary key generator table have unique constraints.<br>If unique constraints do apply to one or more columns in this table, set the value of this attribute to an array of one or more <tt>UniqueConstraint</tt> instances.

<td>By default, EclipseLink persistence provider assumes that none of the columns in the primary key generator table have unique constraints.<br>If unique constraints do apply to one or more columns in this table, set the value of this attribute to an array of one or more <tt>UniqueConstraint</tt> instances.

The [[#Example 18-9|Usage of @TableGenerator]] example shows how to use this annotation to specify the allocation size for the <tt>TABLE</tt> primary key generator named <tt>Emp_Gen</tt>.

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<span id="Example 18-9"></span>

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The following example shows how to use this annotation to specify the allocation size for the <tt>TABLE</tt> primary key generator named <tt>Emp_Gen</tt>.

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''''' Usage of @TableGenerator'''''

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<span id="Example: @TableGenerator"></span>

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======''Example: Using @TableGenerator''======

<source lang="java">

<source lang="java">

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@Entity

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@Entity

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public class Employee implements Serializable {

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public class Employee implements Serializable {

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...

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...

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@Id

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@Id

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@TableGenerator(name="Emp_Gen", allocationSize=1)

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@TableGenerator(name="Emp_Gen", allocationSize=1)

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@GeneratorValue(strategy=TABLE, generator="Emp_Gen")

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@GeneratorValue(strategy=TABLE, generator="Emp_Gen")

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@Column(name="CUST_ID")

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@Column(name="EMP_ID")

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public Long getId() {

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public Long getId() {

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return id;

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return id;

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}

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}

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...

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...

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}

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}

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</source>

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======''Example: Using <code><nowiki><table-generator></nowiki></code>''======

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<source lang="xml">

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<entity class="Employee">

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<attributes>

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<id name="id">

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<column name="EMP_ID"/>

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<generated-value generator="Emp_Gen" strategy="TABLE"/>

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<table-generator name="Emp_Gen" allocationSize="1"/>

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</id>

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...

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</attributes>

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</entity>

</source>

</source>

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<br>

Every table that you use for id generation should have two columns – if there are more columns, only two will be used. The first column is of a string type and is used to identify the particular generator sequence. It is the primary key for all of the generators in the table. The name of this column is specified by the <tt>pkColumnName</tt> attribute. The second column is of an integer type and stores the actual id sequence that is being generated. The value stored in this column is the last identifier that was allocated in the sequence. The name of this column is specified by the <tt>valueColumnName</tt> attribute.

Every table that you use for id generation should have two columns – if there are more columns, only two will be used. The first column is of a string type and is used to identify the particular generator sequence. It is the primary key for all of the generators in the table. The name of this column is specified by the <tt>pkColumnName</tt> attribute. The second column is of an integer type and stores the actual id sequence that is being generated. The value stored in this column is the last identifier that was allocated in the sequence. The name of this column is specified by the <tt>valueColumnName</tt> attribute.

change the initial value to match an existing data model (for example, if you are building on an existing data set, for which a range of primary key values has already been assigned or reserved);

configure the primary key generator's table with a specific catalog or schema;

configure a unique constraint on one or more columns of the primary key generator's table;

For more information, see Section 11.1.46 "TableGenerator Annotation" in the JPA Specification.

@TableGenerator Attributes

Attribute

Description

Default

Required?

name

The name of the generator must match the name of a GeneratedValue with its strategy attribute set to TABLE. The scope of the generator name is global to the persistence unit (across all generator types).

String primary key value for the primary key column in the generator table.

TableGenereator.name

No

schema

The String name of the schema.

Default schema of the database

No

table

A String name of the table in which to store the generated ID values.

SEQUENCE

No

uniqueConstraints

By default, EclipseLink persistence provider assumes that none of the columns in the primary key generator table have unique constraints.If unique constraints do apply to one or more columns in this table, set the value of this attribute to an array of one or more UniqueConstraint instances.

For more information, see Section 11.1.49 "UniqueConstraint Annotation" in the JPA Specification.

No additional constraints

No

valueColumnName

A String name of the column that stores the generated ID values.

SEQ_COUNT

No

The following example shows how to use this annotation to specify the allocation size for the TABLE primary key generator named Emp_Gen.

Every table that you use for id generation should have two columns – if there are more columns, only two will be used. The first column is of a string type and is used to identify the particular generator sequence. It is the primary key for all of the generators in the table. The name of this column is specified by the pkColumnName attribute. The second column is of an integer type and stores the actual id sequence that is being generated. The value stored in this column is the last identifier that was allocated in the sequence. The name of this column is specified by the valueColumnName attribute.

Each defined generator represents a row in the table. The name of the generator becomes the value stored in the pkColumnName column for that row and is used by EclipseLink persistence provider to look up the generator to obtain its last allocated value.